Middle armor block for a coastal structure and a method for placement of its block

ABSTRACT

This invention relates to a middle armor block for a coastal structure and a method of placement of its block with a hydraulic stability of a slope surface and an economical construction cost. The middle armor block of the half-loc comprises a body forming an octagon column with a rectangle side and a perforated hole at the center, a leg integrally formed and attached to alternatively each side of the body and a protruding foot at a lower portion of the leg and each corner of the leg and the foot is chamfered. For a placement type of the blocks, the middle armor block of the half-loc are tilted with a certain angle and each side portion of the leg of the block is contacted to the other side portion of the leg of neighbor block all around directions in series.

CORRESPONDING RELATED APPLICATIONS

This application is a U.S. National Phase of PCT/KR99/00565 filed onSep. 18, 1999, claiming priority to Korean Application No. 1998/38696filed on Sep. 18, 1998.

BACKGROUND OF THE INVENTION

The present invention generally relates to a coastal structure and amethod of its placement. More particularly, the present inventionrelates to a middle armor block for a coastal structure and a method ofplacement of its block with a hydraulic stability of a slope surface andan economical construction cost.

Generally, the coastal structure, which is located inside harbor orleeward, is installed underwater for protecting facility structures fromtransportation of wave energy. When the coastal structure is constructedfor a breakwater or seawall, a sandy rock is used at an under layer ofthe coastal structure for hydraulically stabilizing on the slopesurface, and artificial armor units are used at an upper layer of thecoastal structure, such as a tetrapod, a dolos, an accropode or acore-loc for dissipating wave energy. Specifically, for a design methodof the breakwater, a rubble mound breaker is widely adopted to installthe artificial armor units for the front slope surface. Recently,Caisson adopted a composite type structure for constructing thebreakwater.

Due to the increasing amount of trades and the size of surfacefreighters, there is a tendency to construct the breakwater on thedeeper water advanced from the coast. Therefore, the weight of coatingmaterials is expected to increase for protecting the structure againstbigger waves. For the design of newly developing harbors, the severerweather and the bigger waves should be considered in comparison to thedesign conditions of a conventional harbor.

For protecting the important facilities on the leeward, the breakwateror seawall should be designed with at least a 100 year return period.

According to the conventional standard design method for a section, incase of constructing a large sized harbor, or a conventional rubblemound breakwater and the seawall, a weight ratio of an upper layer ofcoating materials and a lower layer of sandy stones would be 1:1/10.(Coastal Engineering Research Center, U.S. Army Corps of Engineers,1984, Shore Protection Manual Pg. 7-228). It is possible to provide ademanded weight of the coating materials because the coating materialscould be possibly manufactured by an artificial casting. But, it is noteasy to provide enough amount of corresponding weight of the under layerof sandy stones because the natural rocks for under layer of sandystones are usually provided nearby the construction site.

To solve the problems described above, a conventional artificial armorblock or a slightly modified type of block is used instead of the lowerlayer of sandy rocks for the front slope layer coated block. In thiscase, it would not clearly be stable for the hydraulic characteristicsof the whole section if the lower layer were exposed during aconstruction or placed together with the front slope layer coated block.

On the other hand, the Grovel sea level is raised because of the Laninorphenomenon. As a result, it may not be occurred the expected dissipationof wave energy due to wave breaking in the shallow water zone. However,the current design for the coastal structure does not consider theraised sea level.

SUMMARY OF THE INVENTION

An object of this invention is to overcome the problems described aboveand provide an artificial block (hereinafter “half-loc” to replace thesandy stones.

Another object of this invention is to provide a new form of the middlearmor block for improving the ability of construction at theconstruction site and the stability of the breakwater.

Another object of this invention is to provide a safety placement methodwhen a middle armor block is constructed along with the front slopelayer coating material.

In order to accomplish the above objectives of this invention, the newform of the middle armor block comprises a body having a shape ofoctagon column with a rectangle side and a perforated hole at the centerof the top of the body.

Four legs are integrally formed at each of a lower portion of the legsand each corner of the legs and the foot is chamfered.

The other objects and features of this invention will be in partapparent and in part pointed out hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B show a half-loc of embodiments of this invention.

FIG. 2 shows a top view and a front view of the half-loc of oneembodiment of the invention shown in FIG. 1A.

FIGS. 3 to 5 show a method of placement of the half-loc of an embodimentof this invention.

FIG. 6 shows a graph representing a relationship between the Hudsonstability coefficient and the rate of damage depending on the placementof the half-loc.

FIG. 7 shows a graph representing a relationship between the Hudsonstability coefficient and the rate of damage for the placement of thehalf-loc shown in FIG. 3 to FIG. 5.

FIG. 8 shows a graph representing a relationship of the stabilitydepending on the rate of weigh of the half-loc.

The detailed description of this invention will be described inreference to the aforementioned Figures.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A middle armor block of a half-loc (hereinafter “half-loc” according toan embodiment of this invention is shown in FIGS. 1A and 1B. Thehalf-loc mainly comprises a body 10 and a leg 14. The body 10 is formedin the shape of an octagon column with a rectangle side and a perforatedhole 12 at the center of the top surface. The perforated hole 12 has arectangular shape, preferably square. Four legs 14 are integrally formedand attached alternatively to the side of the body 10.

Also, a protruding foot 16 is formed at a lower portion and/or upperportion of the leg 14. The protruding foot 16 is disposed in an upwardor downward direction at each of the top and bottom of the legs. Eachcorner of the lower portion and upper portion of the leg 16 and the foot14 is chamfered.

The perforated hole 12 at the center of the body 10 is designed to passthe water upward or downward to disperse an up-lifting force. Theperforated hole 12 has a square shape. Each side of the perforated hole12 is parallel to the side of the body, which does not have a leg. Theperforated hole 12 is disposed at the center of the top of the body inorder to avoid the concentration of the stress. Each foot 16 formed onthe top and bottom of the leg 14 will be locked in the upper and lowercoated layer rocks of the breakwater or seawall and minimize theslippage. Therefore, it will improve the reinforcement of upper andlower coated layer rocks and increase the stability of the hydrauliccharacteristics. Also, the corners of the leg 14 are chamfered todisturb the water flows over the blocks.

The detailed dimensions of the half-loc of an embodiment as shown inFIG. 1A are shown in FIG. 2.

The maximum length of the half-loc is shown in FIG. 2, i.e., a dimensionC measured from an outside of the leg 14 to the opposite side of the leg14, with an assumed scale of 100. It is favorable for the half-loc tohave a thickness of the leg 14 approximately 20, a width of the leg 14approximately 40, a thickness of the body 10 approximately 30 for thedesirable stability and ability of the construction. Also, it isdesirable for one side length of the perforated hole 12 to beapproximately 20, and the height of the protruding portion of the foot16 from the body 10 to be approximately 5. (Hereinafter the block havingabove dimension is called “block I”.

For a convenient construction of the block, as an alternative embodimentof a half-loc without a top foot as shown in FIG. 1B, a modified form ofthe half-loc is considered to remove the upper extruding foot 16 of theleg 14 during the casting of the block. (Hereinafter the block withoutthe upper foot is called “block 11”.

The volumes of these blocks using the scale “C” for a standard dimensionare representing:

V=0.2134×C ³(Block I)

V=0.19145×C ³(Block II)  (1)

The important factor of construction of the half-loc is a placementtype. The placement type is closely related to the stability of theblock and dominantly related to a degree of interlocking and a porosityof the half-loc.

Therefore, FIGS. 3 and 5 of the present invention show arrangementmethods for the placement type.

The placement type of FIG. 3 (hereinafter “Type I”) shows a method ofhalf interlocking. This method of half interlocking arranges blocks tocontact a pro-outside of leg 14 of one block to an aft-outside of leg 14of a neighbor block in a first serial line, and the left-outside orright-outside of leg 14 of the blocks in a second serial line. Theright-outside or left-outside of leg 14 of the blocks in the neighborserial line are contacted by disposing each leg inside a concave areawhich is created by a serial line, and then coating over the blocks.

The arranged blocks of half-interlocking looks like a honeycomb. Thepro- or aft-outside leg 14 of the neighbor blocks contacting each otherin a serial direction are contacted perpendicular to the left or rightoutside legs 14 of the blocks in the second serial line, and form azigzag arrangement. This method of placement type perfectly links eachblock together to be almost static.

The placement type of FIG. 4 (hereinafter “Type II”) shows anotherarrangement method where the chamfered portions of the legs of theblocks are contacted to the chamfered portions of the legs of theneighbor blocks all around the blocks in the series. The blocks of typeII are disposed individually without a linked relationship to eachother, and have a high porosity.

The placement type of FIG. 5 (hereinafter “Type III”) discloses anotherarrangement method where the side portions of the legs of the block aretilted and contacted to the side portions of the legs of the neighborblocks in the series.

FIGS. 3 to 5 disclose an ideal arrangement of the placement type. Inreality, there are limitations to construct the ideal arrangement of theplacement type at the construction site. However, the actualconstruction should not deviate from the selected ideal arrangement ofthe placement type if possible.

Using the half-lock block shown in FIG. 1, the number of required blockscan be calculated from a given area of the construction site dependingon the selected placement types of Type I, Type II, and Type III. Theporosity can be calculated by counting a height of the top and bottom ofthe blocks.

Using the placement types described above, an experiment for theexposure stability can be performed to apply the actual construction.The data of exposure stability is obtained through the experimentsbecause the coated block would be exposed to the wave during theconstruction.

An experimental section of model is determined by considering theparameters related to the size of the block, the expected stability, thesize of the model and the source of a wave and reservoir. Table 1 showsthe relationship of the above parameters based on the given experimentalconditions.

C (cm) V (cm{circumflex over ( )}3) W (g) K_(D) H_(1/3), cm H_(max), cmD_(g), cm R_(u), cm D_(s) + R_(u) R_(L), cm 5.40 33.60 77.29 3.00 7.6215.33 25.13 18.39 43.52 18.39 5.40 33.60 77.29 4.00 8.39 16.87 27.6520.24 47.90 20.24 5.40 33.60 77.29 5.00 9.04 18.17 29.79 21.81 51.6021.81 5.40 33.60 77.29 6.00 9.60 19.31 31.66 23.17 54.83 23.17 5.4033.60 77.29 7.00 10.11 20.22 33.33 24.39 57.72 24.39 5.40 33.60 77.299.00 10.99 22.10 36.24 26.53 62.76 26.53 5.40 33.60 77.29 10.00 11.3922.89 37.53 27.47 65.01 27.47 5.40 33.60 77.29 11.00 11.75 23.63 38.7428.36 67.10 28.36 5.40 33.60 77.29 12.00 12.10 24.33 39.88 29.20 69.0829.20 5.40 33.60 77.29 13.00 12.43 24.99 40.96 29.98 70.95 29.98 5.4033.60 77.29 14.00 12.74 25.61 41.99 30.73 72.72 30.73 5.40 33.60 77.2915.00 13.03 16.21 42.96 31.45 74.41 31.45

Wherein: C is the basic scale of the half loc.

V is the volume.

W is the weight.

K_(D) is the Hudson's stability coefficient.

H_(⅓) is the significant wave height.

H_(max) is the maximum wave height.

D_(s) is the water depth of the front slope surface.

R_(u) is the run-up height.

D_(s)+R_(u) is the height of the block.

R_(L) is the height of free board.

From each of the parameters described above, a weight of the half-loccould be calculated, and then the height of a wave corresponding to thevalue of the expected stability could be calculated for the design ofexperimental conditions. The volume of the half-loc could be calculatedfor the design of experimental conditions. The volume of the half-loccould be calculated from the equation 1 by using the basic scale of “C.”After the volume is determined, the corresponding weight of the half-loccould be calculated.

The significant wave height H_(⅓) could be calculated based on theHudson's stability coefficient K_(D). (For the Hudson's stabilitycoefficient K_(D) refer to “Laboratory Investigation of rubble moundbreakwater,” 1965, Proc. ACSE, vol. 85). Hudson suggests an equation forthe Hudson's stability coefficient K_(D) as shown below.

K _(D)=γ(H _(⅓))³ /W(S _(r)−1)³cot θ  (2)

Wherein: W is the weight of armor block.

γ is the specific weight of concrete in the air.

(2.657 g/cm³ for granite, 2.5 g/cm³ for concrete)

S_(r) is the specific gravity of concrete against the seawater.

cot θ is the slope.

The K_(D) value is set up in a range of 3 to 12. This range of the valueis quoted from the blocks used for other purposes because there are noprevious examples or data available for the middle armor block. AnX-block, such as an all side slope coating material or a solid blockdeveloped by Japanese company TETRA, suggests a K_(D) value of 10. It ishard to estimate the hydraulic stability because the rate of porosityvaries depending on the placement types. For the smooth slope, the K_(D)value is estimated to be in the range of 4 to 5 based on the K_(D) valueof 10 based on the X-block as a standard value. This invention of thehalf-loc is designed to use the block on a slope rate of 1:1.5.Therefore, the K_(D) value is in the stable range for the smooth slope.From the TABLE 1, the value of H_(⅓) is in the range of 9.60˜13.03 cm.

An equation having a relationship between the maximum wave heightH_(max) and the significant wave height H_(⅓) is introduced in the“Random Sea and Design of Maritime Structures” 1990, 16 section, byYoshimi Goda. The equation of the wave height ratio is given:

(H _(max) /H _(⅓))_(mean)=0.706{[In N ₀]^(½)+(2[In N ₀]^(½))}  (3)

Wherein: N₀ is a frequency of wave and is used 1,000 waves.

The water depth of the breakwater is estimated based on the calculationof H_(max) using the equation 3 in order not to break the wave. In thisexperiment, a possibility of breaking wave by the standing waves isconsidered and used the value of D_(s)=H_(max)/0,61 instead of using thevalue of D_(s)=H_(max)/0,78 which is shown in the McCowan's “On theSolitary Wave” (Philosophical magazine, 5^(th) series, vol. 32, No. 194,PP 45-58) and related to a limitation of wave breaking of a solitarywave and a water depth.

Also, the run-up height R_(u) is estimated in order to determine theheight of free board R_(L). The value of the run-up height R_(u) isreferenced from the Wallingford, “Hydraulic Experiment Station,” 1970,“Report on Tests on Dolos Breaker in Hong Kong,” and the experimentaldata of the run-up height for Dolos from Gunbak A. R., (“Estimation ofincident and reflected waves in random wave experiments,” 1977, Div.Port and Ocean Engineering, Rep. No. 12/77, Tech, Univ. of Norway,Trondheim). The maximum cycle of 2.5 sec is selected for a cycle T. Themodel section and the wave height are finally decided after verifyingthat the sum (95.91 cm) of the height of the block (D_(s)+R_(u)=74.41cm) and the mound height (21.5 cm) is less than the height of a watertank (120 cm).

The water depth of the front surface D_(s) for the experimental model of43 cm and the front slope of 1:1.5, which is widely used, forconstruction of the coated slope breakwater of the tetrapod is selected.The thickness of the front slope of 2.16 cm, which corresponds to 40percent of C—5.3 cm, and the weight ratio of the first lower layer andthe second lower layer of 1:20 are selected. The thickness of thestandard section of the lower layer corresponds to the thickness of thesecond lower layer. Based on these relationships, the model is used tosimulate a natural rock having 1.4 cm thickness corresponding to theaverage diameter and the height of free board R_(L) 32 cm.

The model width of the upper layer is decided by an experimentalproportion because the model is not a real block, and there is noproportional simulation available. The purpose of this experiment is todetermine the weight ratio and develop the middle armor block of thehalf-loc instead of using the natural stones of sandy rock nearby theconstruction site. The Froude equation is related to the weight ratioand length ratio of Wr=1r3. The estimated proportion ratio of 1:28.85 iscalculated based on the 77.29g of block, 0.7m³ of sandy rock and 1.855ton of the corresponding weight. (2.65 ton/M³ of specific volume-weightis used for calculation). By this time, a space of 6 m (=3 m×2 way) fortwo-way traffic would be provided on top of the block. Therefore, thesize of the model would be 20.8 cm. The width of road 3.0 m is usedaccording to the Standard Design of Harbor Facility.

The middle armor block of the half-loc is coated double raw in case theupper layer of the block is coated with the front slope coatingmaterial, such as T.T.P. Rear slope ratio is 1:1.5, i.e. the same as thefront slope ratio. In this experiment, only the core sandy rocks areused due to the non-overtopping test.

There are two kinds of wave generators: Position Type and AbsorptionType can be used in the experiments. An absorption Type of wavegenerator is used for this experiment.

Due to the non-overtopping test, the waves which have the significantwave height (H_(⅓)) and spectrum are generated corresponding to thetheoretical value of the spectrum at the location of the disposed block.Each of the experiments is classified depending on the kind of waves byusing the data from TABLE 1. T_(⅓) is tested between the range of1.0˜2.5 sec with 0.5 sec increment for the range of 6˜14 cm of waveheight with 2 cm increment. The experiment is performed for total 20kind of waves by fixing the water depth (43 cm) of the all slope surfaceD_(s) and varies the values of T_(⅓) and H_(⅓.)

A locking and displacement of the middle armor block of the half-loc ismainly continuously observed by increasing the wave height for eachperiod of experiment. The experiment is continued by increasing the waveheight for each period until the model of the breakwater or the lowerportion of the sandy rock is damaged. Then, the wave height is recordedwhen the model is damaged.

A calculation of damage ratio is the total number of blocks divided bythe accumulated number of blocks, which corresponds to the Hudson'sstability coefficient K_(D) and the significant wave height H_(⅓). Theequation would be:

 D=n/N×100(%)  (4)

Wherein: D is a damage ratio.

n is accumulated number of blocks until the

highest wave.

N is the total number of the blocks.

FIG. 6 represents the stability obtained from the experiments for BlockI and Block II. According to the test results shown in FIG. 6, the BlockI is more stable than the Block II in all range of waves. Specifically,when the Block II is coated with Type I, the damage ratio would reach 4percent. It is revealed that the Block I coated with Type I has thehighest damage ratio. Except the Type I, all other models haveapproximately 11.0 of the K_(D) value. Block II is easier to construct,but is less stable than Block I. Therefore, Block I has improvedstability and anti-slip when all slope coated block is placed on theupper layer.

FIG. 7 represents the test results obtained from the experiments forBlock I, Type I, Type II, and Type III. According to the test results,Type I and Type III had a damage ratio of 1 percent corresponding to4.96 K_(D) of the wave height. Type II received no damage until thewaves reach corresponded to 11.38 K_(D) of wave height.

For each porosity of 33.3%, 37% and 33% for Type I, Type II and TypeIII, the exposure stability was analyzed and compared with each other.The test results reveal that Type III is the most stable placement type.

In addition to the stability depending on the placement type of thehalf-loc block, another important factor is a weight calculation of thehalf-loc block for the lower layer coating material.

According to the conventional standard design, a weight ratio of eachsection is suggested. For example, a weight ratio 1:10 is used for allside slopes coating material block. In this invention, the weight ratiohas determined through the experiment to establish the stability for theall side slopes coating material block.

To determine the weight ratio, the experiment is performed for thestability of all side slope coated blocks using Type II, which is themost stable placement type, and Type III, which is the least displacedtype and easiest to construct. The reason why Type III is selected isthat it maintains the most stability for the half-loc coated block andthe lowest porosity of the placement type. If the blocks would bedisplaced, it will affect the stability of the all side slope coatedblock.

The tetrapod is used for all side slope coated block. According to thisinvention, the weight ratios of the half-loc coated blocks tested are3.36, 5.25, 6.70 and 10. FIG. 8 represents the test results for the fourcases of non-breaking, K_(D)=10.2 for Hudson's stability coefficient,corresponding to 150% of the biggest wave based on the normal wave.

As shown in FIG. 8, the four kinds of the weight ratios are all stable.The bar graph of FIG. 8 represents that, for example, Run Group 2, thetetrapod and the bottom portion of the half-loc coated block of thisinvention is impacted by 1,000 waves of 2.0 cycles, followed by theimpact of 1,800 waves of 2.5 cycles. As a test result, each wave of thecontinuation time exceeds more than 1,000 waves. The breakwater wouldusually be impacted by 1,000 waves of 3˜4 impacting hours during arainstorm. Therefore, this experiment chooses the stable condition offour cases estimating at least 1,800 waves and 2.0-2.5 cycles.

The half-loc coated block of this invention, which is coated by thetetrapod using 3 to 10 times of weight, is in a stable condition.

According to the test results, the half-loc coated block of thisinvention could be replaced for the natural stones conventionally usedin the slope type breakwater. The half-loc coated block of thisinvention improves the efficiency and standardization of the placementtype, the lower layer and upper layer coating blocks, and theconstruction method.

The half-loc coated block of this invention solved problem in theconventionally slope type breakwater, calculated the stability dependingon the placement type and provided a new concept of the coastalstructure.

The scope and spirit of this invention is not limited to the descriptionof this invention. It is possible for one who has a skill in the art tomodify or deviate from the structure recited therein, without extendingbeyond the scope and spirit of this invention.

What is claimed is:
 1. A middle armor block of a half-loc comprising: abody having a shape of octagon column with a rectangle side, said bodyhaving a square-shaped perforated hole at the center; four legs having ashape of rectangle column on four sides of said body alternatively, saidlegs being integrally formed to said body; and a protruding foot formedat each of an upper portion and a lower portion of said legs, eachcorner of said legs and said protruding foot being chamfered.
 2. Themiddle armor block of half-loc as claimed in claim 1, wherein said legsare measured with a basic dimension of C, a thickness of said legs is0.2 C, a width of said legs is 0.4 C, and a thickness of said body isless than 0.4 C, wherein the total volume of said block using the scale“C” for a standard dimension satisfies the equation V-kC³, k being inthe range of about 0.18 to about 0.3.
 3. A middle armor block of ahalf-loc comprising: a body portion including a hole perforating from atop surface to a bottom surface; at least four legs projecting from eachof four side surfaces of said body portion; and at least one foot formedon a bottom surface of each of said legs, wherein said body portion incombination with said legs has a substantially octagonal shape.
 4. Thearmor block as claimed in claim 3, further comprising: at least one footformed on a top surface of each of said legs.
 5. The armor block asclaimed in claim 3, wherein each of said legs has a thickness of 0.2 Cand a width of 0.4 C, and wherein said body portion has a thickness lessthan 0.4 C.
 6. The armor block as claimed in claim 3, wherein said holeis adapted to pass water upward or downward through said body portionfor dispersing an up-lifting force.
 7. The armor block as claimed inclaim 3, wherein said hole is substantially square.
 8. The armor blockas claimed in claim 3, wherein said side surfaces are substantiallyparallel to a central axis of said hole.
 9. The armor block as claimedin claim 3, wherein a weight ratio of said half-loc to an artificialarmor block is 1:3^(˜)10 when said half-loc is disposed under saidartificial armor block.
 10. A method of stacking a plurality of armorblocks of a half-loc, comprising the steps of: placing a first armorblock in a location to resist water flow; and interlocking a leg of asecond armor block with a leg of said first armor block, wherein each ofsaid first armor block and said second armor block comprises: a bodyportion including a hole perforating from a top surface to a bottomsurface; at least four legs projecting from each of four side surfacesof said body portion; and at least one foot formed on a bottom surfaceof each of said legs, wherein said body portion in combination with saidlegs has a substantially octagonal shape.
 11. The method of stacking asclaimed in claim 10 further comprising the steps of: tilting said secondarmor block with a certain angle; and contacting each left or right sideof said legs of said first armor block to respective right or left sidesof neighbor legs of said second armor block.
 12. The method of stackingas claimed in claim 10, wherein said plurality of armor blocks arearranged in series rows by said interlocking step.